Bathroom above a garage...

I just completed my attached garage, which is attached by a one and a half story breezeway, and I want to plumb it out before finishing the 12x12 downstairs of the breezeway. I would like to have a full bath above the garage, but I don't know how to drain it. The floor joists are running the wrong way to get into the common wall to go down to the full basement. The floor joists are 2x10, but I think it's risky to bore even a 3" hole sloping through them. The breezeway has two floors and will be heated. The downstairs of the garage will not be heated. Is there any way to solve the problem without running the drain pipes under the floor joists rather than through them?

How do I run the drain from above the garage to the pipe in the basement? I have to run it about 15 feet horizontally before hitting the common wall with the house where I can run it down into the basement.

Running drain's through an unheated area is not normally a problem.
Drains installed properly either have running water in them or, drain dry after use. Hence they will not freeze.

If the pipes are clogged, have a sag that holds water, or, there is a low volume of water leaking down the drain, I.E. dripping faucet, or leaking flapper, there may be a possibility of freezing as the volume of water will be insufficient to stay warm before it freezes.

whether heated or unheated, do you have a solution on how to move the 15 feet horizontally to the common wall with the house? Is the only solution running it under the second floor joists and boxing it in?

Where does the main drain line go when it leaves the house? Might be a pain now, but you could just run it down through the floor to underneath and then connect to the main drain rather than doing it after running over to the main house.

The main drain leaves the house at the opposite side from the garage. Just inside the house from the common wall is a downstairs bathroom and a 4 inch pipe that can be tied into. It's just a matter of getting to it.

If I understand your layout correctly, the drain will be in the garage. It seems to me the logical way to do this is to suspend the drain under the joists and just leave them exposed. But no matter how you do it, there must be a slope of at least 1/4" per foot on the horizontal run.

The main drain leaves the house at the opposite side from the garage. Just inside the house from the common wall is a downstairs bathroom and a 4 inch pipe that can be tied into. It's just a matter of getting to it.

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Think outside the box for a moment. Should you do the connection outside of the house?

Not to be beligerent, but your problem is why God made plumbers and why we go to school for as long as we do. A plumber doing the work might have more than one option to install it, but we cannot without seeing the job. Drilling through the joists, however, would be the very last one, if it was even considered.

That's what I was getting at...if the drain runs by the garage, make a new one on the main line to the road, forget about getting it into the basement and across the entire garage...just go under to where you need to go. Or, run it across the ceiling, then down the wall to where you originally planned.

I would have to rip up a patio to do that, and I am not sure if I would have enough drop to keep the 1/4 inch per foot drop. Inside the box (house) I can keep a higher elevation until I drop into the basement. I appreciate the suggestion, but don't think it would be a better solution here. The only thing I can think of is dropping it below the floor joists and boxing it in for aethetics..

Maybe you can run through the joist space to a side wall then run underneath the joists at the wall. That will help to make the box less obtrusive. But then again, I have all kinds of pipes in the ceiling of my garage and use them to hang stuff...

When I broke into plumbing, they didn't let me touch waste and vents for the first year.
After I had been running copper water lines for a long time, then they started showing me the why's and why not's of waste and vents.

Water supply can go up and down and around things.

Waste can only go downhill, and not many bends without adding cleanouts. In fact anything over 135 degrees requires a cleanout.

Most plumbers would drop the waste below the 2x10's for the water closet line.
No sense hacking them up.

To give some who are lacking in some other area a feeling of self-importance.

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Hey! I represent that remark.

I did read on a web site that one of the ten most hard to fill jobs was plumbing. It seems onbody wants to do it, heck, even I don't want to do it.
People are hassling me about studying on how to be a plumber, that heck, I'm just going to write a book on how you should do life in general. I figure that's easier than plumbing for a living. It will be like a answer to all your questions book.

I did read on a web site that one of the ten most hard to fill jobs was plumbing. It seems onbody wants to do it, heck, even I don't want to do it.
People are hassling me about studying on how to be a plumber, that heck, I'm just going to write a book on how you should do life in general. I figure that's easier than plumbing for a living. It will be like a answer to all your questions book.

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Where I grew up, a middle class suburb of Boston, the wealthiest guy on the street was a plumber. My best friend became a plumber and worked for him for a while.

When I broke into plumbing, they didn't let me touch waste and vents for the first year.

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That's the way I remember it too.

My father (Pap) wanted all of us to go to college, but he also felt it was important for us to at least have a go at a trade. He was a mechanic, but he understood and could apply algebra and trig better than I ever will. I will never forget him looking at one of brothers as he described a boat lift he wanted to build and, rather sternly saying: "Son, have you forgotten Bernoulli's principle?" That brother went on to be a fine electrician.

Me, I learned how to run copper. I learned how to lead joints, but never really got good at it. I'm much better at punching holes in the ground, but I digress.

Why did god make plumbers? To protect the health of the nation and to strike fear in the hearts of carpenters every time they reach for the sawzall.

To paraphrase the Irish saying.
Lord grant me the ability to do the plumbing I can do.
Lord grant me the serenity to call a plumber to do the things I cannot/should not do.
And, Lord let there be a forum to tell me the difference.